Fix build when ant.tstamp.now is not specified

build.xml

@@ -2879,7 +2879,7 @@ skip.installer property in build.properties" />
     <taskdef name="repeatableArchive"
              classname="org.apache.tomcat.buildutil.RepeatableArchive"
              classpath="${tomcat.classes}" />
-    <repeatableArchive datetime="${ant.tstamp.now}">
+    <repeatableArchive datetime="${tstamp.file}" pattern="yyyy-MM-dd HH:mm:ss">
       <fileset dir="${tomcat.dist}/webapps/docs">
         <include name="**/*.zip"/>
       </fileset>

java/org/apache/tomcat/buildutil/RepeatableArchive.java

@@ -23,6 +23,9 @@
 import java.nio.file.Files;
 import java.nio.file.StandardCopyOption;
 import java.nio.file.attribute.FileTime;
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.util.Date;
 import java.util.Enumeration;
 import java.util.LinkedList;
 import java.util.List;
@@ -48,7 +51,8 @@ public class RepeatableArchive extends Task {
 
     private final List<FileSet> filesets = new LinkedList<>();
 
-    private long datetime;
+    private String datetime;
+    private String pattern;
 
     /**
      * Sets the files to be processed
@@ -60,16 +64,29 @@ public void addFileset(FileSet fs) {
     }
 
 
-    public void setDatetime(long datetime) {
+    public void setDatetime(String datetime) {
         this.datetime = datetime;
     }
 
 
+    public void setPattern(String pattern) {
+        this.pattern = pattern;
+    }
+
+
     @Override
     public void execute() throws BuildException {
 
+        SimpleDateFormat sdf = new SimpleDateFormat(pattern);
+        Date date;
+        try {
+            date = sdf.parse(datetime);
+        } catch (ParseException e) {
+            throw new BuildException(e);
+        }
+
         byte[] buf = new byte[8192];
-        FileTime lastModified = FileTime.fromMillis(datetime);
+        FileTime lastModified = FileTime.fromMillis(date.getTime());
 
         for (FileSet fs : filesets) {
             DirectoryScanner ds = fs.getDirectoryScanner(getProject());